ay Leno can laugh at himself, which is just as well. His autobiography was called Leading With My Chin, a reference to the huge jaw that protrudes from his face. His rival TV chat show host David Letterman refers to him as 'Jay Big Jaw Leno'. If he didn't crack the TV game, he might well have made it as an understudy for Lou Ferrigno, the man who played the Incredible Hulk.

Leno can take it, but he also dishes it out in oodles. Since succeeding Johnny Carson as host of NBC's Tonight Show in 1992, Leno has carved out a niche as the US's favourite talk show host. In a move that turned out to be disastrous, he stepped aside for young gun Conan O'Brien a few years ago, but had to return to save the show, and by extension, the station.

No skeletons have ever emerged from his closet. No hookers, no cocaine, no allegations of sexual assault and no demented tales of neglected childhood being retailed by skint siblings. The man is as clean as a whistle, which isn't necessarily a good thing in a comedian.

Controversy has not totally eluded him. In 2005, he gave evidence at Michael Jackson's trial for child molestation, suggesting that the family of Jackson's accusers were operating from a script. He also came into conflict with the screenwriters' guild during a strike in 2008 when he wrote his own scripts, contrary to the rules. Shock jock Howard Stern has accused him of stealing material.

Leno is paid over $30m a year, but his only display of ostentatious wealth is his automobile collection, which is reputed to number over 80, and is kept in warehouses near his California home.

He is a sharp political commentator and an equal opportunities joker, refusing to take sides in the US political divide, unlike his fellow funny man, Jon Stewart.

Perhaps it was his political antennae that sought out Brian Cowen as the butt of a joke on the 22 September episode of the show.

Using a photo of Cowen which was far from flattering, he asked the audience whether this man was a bartender, politician or a comedian. To hoots of audience laughter, he told them in a silly attempt at an Irish accent that the man was the prime minister of Ireland. "Good to know that it's not just here we have drunken morons," he said.

Even by Leno's standards, the insult was over-the-top. He often, for instance, made reference to George W Bush's alleged drinking, but never in such base language. You wouldn't mind, but Dubya really was a moron.

Irrespective of how Cowen's performance as Taoiseach is viewed, insulting him in that manner was little short of bullying for a cheap laugh. Far from being irreverent, Leno is careful about which hackneyed stereotypes he uses. He wouldn't dare make a Jewish Shylock joke about Bernie Madoff, or use the offensive stereotype of lazy Mexicans as material. Neither would he have described Bush in such base terms, whenever touching on the former president's alleged lurch from the wagon while he was president.

But Ireland is thousands of miles away, a minor country, and while the Taoiseach and this country are but specks on the jaw of Leno, America and all its works loom large over here.